Hsp70 in the inferior colliculus of Fischer-344 rats: e¡ects of age and acoustic stress Robert H. Helfert a;b; Ã , Frank R. Glatz III a , Teresa S. Wilson a , Vickram Ramkumar b , Larry F. Hughes a;c a Department of Surgery, Southern Illinois University School of Medicine, P.O. Box 19638, Spring¢eld, IL 62794-9638, USA b Department of Pharmacology, Southern Illinois University School of Medicine, P.O. Box 19638, Spring¢eld, IL 62794-9638, USA c Center for Alzheimer Disease and Related Disorders, Southern Illinois University School of Medicine, P.O. Box 19638, Spring¢eld, IL 62794-9638, USA Received 30 January 2002; accepted 25 April 2002 Abstract Heat shock proteins 72 and 73 (hsp72 and hsp73) were studied in the inferior colliculus (IC) of Fischer-344 rats to determine if their levels are altered during normal aging and following exposure to intense acoustic noise. Three age groups of rats (3, 18, and 25 months) were exposed to ambient sound (control) or broad-band noise at 108 dB sound pressure level (0.0004 dyn/cm 2 ) for 30 min. Western blotting procedures were used to measure hsp72 and hsp73 in ICs and cerebella (positive control). Immunohistochemistry was performed using 3-month olds to study the localization patterns of hsp72 and hsp73 in both structures. The IC and cerebellum exhibited immunolabeling over neuronal somata and proximal dendrites. Ambient levels of hsp72 in supernatants from aged rats were reduced 56.5% þ 7.8% in the IC relative to 3-month olds. This decrease may render the IC more susceptible to stress-related damage. An increase in constitutive hsp73 (350.7% þ 70.4%) was observed in IC pellet fractions from animals exposed to the 108-dB noise when compared to the ambient-noise controls, suggestive of a lipoprotective role for hsp73. This elevation was consistent across age groups. No noise-induced changes in hsp72 were detectable in the IC, indicating that loud sounds may not be an appropriate stimulus for hsp72 induction in this structure. ß 2002 Elsevier Science B.V. All rights reserved. Key words: Auditory; Cerebellum; hsp72; hsp73; Noise; Immunocytochemistry; Western blot 1. Introduction Previous studies have shown that the inferior collicu- lus (IC) of Fischer-344 (F344) rats undergoes structural and chemical changes with age that could adversely a¡ect its function. Among these changes, a balanced loss of excitatory and inhibitory synapses occurs in the central nucleus of the IC with age in the absence of a coincident loss of neurons (Helfert et al., 1999). The synaptic reductions are linked, however, to a cor- responding loss of dendrites. The dendritic losses observed in the IC may be largely the result of degenerative processes intrinsic to this structure. Several studies have shown that the IC is one of the most metabolically active areas of the brain (Sokolo¡ et al., 1977; Gross et al., 1987; Zeller et al., 1997). Under normal, ambient conditions it is subject to greater amounts of oxidative stress during aging as a result of declines in the activities of its antioxidant en- zymes (Mei et al., 1999). As antioxidant enzyme activity is regulated by growth factors via the TrkB receptor, decreases in levels of the latter similar to those observed in the IC of aged rats by Sato et al. (2001) could explain in part the decline in antioxidant enzyme activity and 0378-5955 / 02 / $ ^ see front matter ß 2002 Elsevier Science B.V. All rights reserved. PII:S0378-5955(02)00487-2 * Corresponding author. Tel.: +1 (217) 545 0860; Fax: +1 (217) 545 0145. E-mail address: rhelfert@siumed.edu (R.H. Helfert). Abbreviations: ANOVA, analysis of variance; F344, Fischer-344; HSD, honestly signi¢cant di¡erence; hsp70, 70 000 molecular weight family of heat shock proteins; hsp72, 72000 molecular weight heat shock protein; hsp73, 73 000 molecular weight heat shock protein; IC, inferior colliculus; PBS, phosphate-bu¡ered saline; Tris^HCl, tris[hydroxymethyl]-aminomethane hydrochloride Hearing Research 170 (2002) 155^165 www.elsevier.com/locate/heares